In fact someone has already got an extension for the Vango Aspen on here... have a look at the pictures on the review section here its picture 4 as you can see they have a vango generic extension
The single pole Vango canopy is only useful to stop rain getting into a sloping door. It isn't really long enough to sit under or store anything. I would choose the two pole one, and you can get them with a door on as well.